Experimental and theoretical study of the photofragmentation process: Ar-3(+)+h nu -> Ar-2(+)+Ar

An experimental study of the photofragmentation of Ar-3(+) at wavelengths > 650 nm has been undertaken in order to investigate the reaction channel Ar -3(+)+h nu --> Ar-2(+)+Ar. As a function of photon energy, measurements hav e been made of the Ar+/Ar-2(+) branching ratio and the relative kinetic ene rgy of the photofragments. A steady decline observed for the latter as a fu nction of decreasing photon energy, suggests that the dimer ions emerges fr om the photodissociation processes with a very high level of internal excit ation. Supporting semiclassical calculations of the decay dynamics confirm the trend seen for the Ar+/Ar-2(+) branching ratio, but do not reproduce th e quantitative details. The calculations do, however, provide strong suppor t for an experimental analysis of the energetics of fragmentation, and show that Ar-2(+) can appear either in the electronic ground state, but with a very high degree of vibrational excitation, or in the weakly bound (2)Pi(g) electronic excited state. (C) 2000 American Institute of Physics. [S0021-9 606(00)01230-7].